TH‐A‐141‐06: Optimization of Incident X‐Ray Source Spectrum Through Filtration for a Benchtop X‐Ray Fluorescence Computed Tomography (XFCT) System

N. Manohar, B. Jones, S. Cho

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: To optimize acquisition of fluorescence photon signal from gold nanoparticles (GNPs) and reduce the effect of Compton scatter in benchtop x‐ray fluorescence computed tomography (XFCT). Methods: In polychromatic XFCT, fluorescence signal is obscured by Compton scatter of source photons, and thus the choice of source spectrum is crucial. An experimental XFCT system for irradiation of a GNP‐containing small animal‐sized phantom was accurately modeled using the MCNP5 code for Monte Carlo simulations. The model used either a lead (Pb) or tin (Sn) filter to harden the 105 kVp source spectrum, and was validated with fluorescence/scatter profile measurements. Spectra (Pb: 1, 2, and 3 mm; Sn: 0.9, 1, 2, and 3 mm) were input into the model and their effect on fluorescence production/detection was investigated. Simulations were also run with hypothetical quasi‐monochromatic x‐ray sources (81, 85, 90, 95, and 100 keV) to determine the ideal energy for discriminating gold K‐shell fluorescence peaks from Compton scatter background. Fluorescence signal‐to‐dose ratio (FSDR) and relative scan time (RST) were used to assess the degree of optimization during simulations. Results: For both materials, increasing filtration hardened source spectra and significantly decreased fluence available for producing fluorescence photons, while increasing FSDR. The RST increased at a much higher rate for a given increase in FSDR. Compared to Pb, Sn produced generally higher overall fluence, more prominent fluorescence peaks, favorably harder scatter profiles, increased FSDR, and shorter RST. Simulations using hypothetical quasi‐monochromatic spectra showed that increasing source energy, between 81 and 100 keV, increased signal‐to‐background ratio and FSDR. Conclusion: Judicious choice of filter material/thickness to tailor polychromatic x‐ray spectrum, considering trade‐offs between FSDR and RST, can dramatically improve the performance of benchtop XFCT. This work will foster the further development of a benchtop XFCT system for routine pre‐clinical imaging applications with GNPs.Supported by NIH/NCI grant R01CA155446; NIH/NCI grant R01CA155446.

Original languageEnglish (US)
Pages (from-to)523
Number of pages1
JournalMedical physics
Volume40
Issue number6
DOIs
StatePublished - Jun 2013

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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